Antibiotic therapy plays a vital role in modern medicine. The advent of antibiotic therapy in this century has, in part, been responsible for the increased life expectancy, as well as lower instances of infant and child-birth deaths. While there are numerous classes of antibiotics available, the semi-synthetic penicillins, the tetracyclines, erythromycins and cephalosporins are probably the most widely used antibiotics.
Despite the availability of a variety of highly effective antibiotics, the search for improved agents is a continuing one for a variety of reasons. Many organisms become resistant to a particular antibiotic or class of antibiotics and thus new drug entities must be continually made available to treat infections involving strains of organisms which have become resistant to all other therapy. Apart from the problem of resistance, this powerful class of drugs have a number of undesirable side effects and thus the search continues for agents which are lower in toxicity than presently available antibiotics yet are effective antimicrobial agents.
Another problem with current antibiotic therapy is that there are certain organisms, such as the genus proteus of organisms, which are very difficult to treat. Thus researchers are constantly seeking new entities which would be effective against various proteus strains.
Recently a new class of antibiotics has been identified and designated as the fortimicins. To date, two fortimicin antibiotics are known, fortimicin A and fortimicin B. Both antibiotics are fermentation products and thus are difficult and expensive to manufacture.
Fortimicin A exhibits a wide range of in vitro activity against gram-positive and gram-negative bacteria and also exhibits excellent activity against strains of Staphylococcus aureus and Escherichia coli which is resistant to various known antibiotics such as kanamycin, gentamicin, tobramycin and the like, as well as exhibiting antibacterial activity against bacteria of the genus Proteus. In vivo tests indicate the ED.sub.50 of fortimicin A against Escherichia coli Juhl KY 4286 in mice to be 6 mg./kg. (See U.S. Pat. No. 3,976,768).
Fortimicin B also exhibits in vitro antibacterial activity against various gram-positive and gram-negative antibiotics, but is considerably less active than fortimicin A. (See U.S. Pat. No. 3,931,400.)
While fortimicin A is a promising lead in the class of fortimicin antibiotics, it has been found that the 4-N-alkylfortimicin B derivatives are generally more stable, but just as effective as fortimicin A.
The present invention provides a novel series of intermediates which are useful in preparing the 4-N-alkylfortimicin derivatives and also provides a method of converting fortimicin B to fortimicin A.